Good water softners help a lot. The well we are on is nasty, heavy iron content in it. We have an iron filter and a 50K grain softner. After installing both I tested the water and found the hardness was down to acceptable levels for a tankless heater. I forgot what the measurements were though, that was 2 years ago. So far havent had a problem with it, nor have I seen any buildup around my faucets like I did before installing the softner/filters.